The present invention relates generally to integrated circuit (IC) fabrication equipment. More particularly, the present invention relates to a pellicle and a method of manufacturing a pellicle.
Semiconductor fabrication techniques often utilize a mask or reticle. Radiation is provided through or reflected off the mask or reticle to form an image on a semiconductor wafer. The wafer is positioned to receive the radiation transmitted through or reflected off the mask or reticle. The image on the wafer corresponds to the pattern on the mask or reticle. The radiation can be light, such as ultra-violet light, vacuum ultra-violet (VUV) light and deep ultra violet light. The radiation can also be x-ray radiation, e-beam radiation, etc.
Generally, the image is utilized on the wafer to pattern a layer of material, such as, photoresist material. The photoresist material can be utilized to define doping regions, deposition regions, etching regions, or other structures associated with an integrated circuit (IC). A conventional lithographic system is generally utilized to project the image to the wafer. For example, a conventional lithographic system includes a source of radiation, an optical system, and the reticle or photomask. The source of radiation provides radiation through the optical system and through or off of the mask or reticle. A pellicle can be employed between the light source and the wafer (i.e., between the mask and the wafer).
Generally, conventional fabrication systems which utilize wavelengths of 193 nm or more include the pellicle to seal off the mask or reticle to protect it from airborne particles and other forms of contamination. Contamination on the surface of the reticle or mask can cause manufacturing defects on the wafer. For example, pellicles are typically used to reduce the likelihood that particles might migrate into a stepping field of a reticle in a stepping lithographic system. If the reticle or mask is left unprotected, the contamination can require the mask or reticle to be cleaned or discarded. Cleaning the reticle or mask interrupts valuable manufacturing time and discarding the reticle or mask is costly. Replacing the reticle or mask also interrupts valuable manufacturing time.
The pellicle is generally comprised of a pellicle frame and a membrane. The pellicle frame may be comprised of one or more walls which is securely attached to a chrome side of the mask or reticle. Pellicles have also been employed with antireflective coatings on the membrane material.
The membrane is stretched across the metal frame and prevents the contaminates from reaching the mask or reticle. The membrane is preferably thin enough to avoid the introduction of aberrations, and to be optically transparent and yet strong enough to be stretched across the frame. The optical transmission losses associated with the membrane of the pellicle can affect the exposure time and throughput of the lithographic system. The optical transmission losses are due to reflection, absorption and scattering. Stretching the membrane ensures that it is flat and does not adversely affect the image projected onto the wafer.
The membrane of the pellicle generally covers the entire printable area of a mask or reticle and is sufficiently durable to withstand mild cleaning and handling. Conventional membrane materials are preferably configured to be stable enough to retain their shape over long periods of time and many exposures to flashes of radiation. Membrane materials are typically thin polymer films that do not appreciably change the optical projection of the lithographic system and that do not contribute to pattern misplacement and other imaging aberrations. The membrane materials should also be inexpensive enough to be cost effective. The membrane can be manufactured from nitrocellulose and have a thickness of 1 to 15 micrometers (typically approximately 2.9 micrometers).
Other pellicle membrane materials include polymers, such as, flouropolymers or cellulose acetate which can be coated with one or more layers of fluoropolymers (anti-reflective coatings (ARC)). The average transmissions of a pellicle with a 2.9 micrometer thick nitrocellulose membrane and an anti-reflective coating can be approximately 99 percent at wavelengths of 350-450 nm. Another conventional pellicle material includes Mylar(copyright) polymer material.
Small particles that adhere to the pellicle surface (the membrane) generally do not significantly obstruct light directed to the surface of the wafer. The metal frame ensures that a minimum stand-off distance from the mask is provided to ensure that no more than a 10% reduction in light intensity on the wafer surface is achieved for a particle of a particular size. The pellicle also keeps particles out of the depth-of-field of the lens. Thus, the stand-off distance prevents contaminates from being effectively imaged onto the wafer.
Adhesive materials can be utilized to attach the pellicle membrane to the frame and the frame to the reticle or mask. Compressive material such as silicone or other natural and synthetic rubbers can be utilized as adhesives.
Membranes made of nitrocellulose, and Mylar(copyright) have limited usefulness in deep UV applications because both exhibit strong absorption near 300 nanometers. In addition, these materials can change color when exposed to deep UV light. Conventional membrane materials, such as, thin polymer films, are not transparent after repeated use at vacuum ultraviolet (VUV) (100-180 nm) wavelengths. For example, VUV radiation provided through the pellicle can discolor and degrade the membrane.
Thus, there is a need for a pellicle which does not utilize conventional materials. Further still, there is a need for a pellicle which is more durable or stable than conventional materials. Further still, there is a need for a pellicle optimized for use in deep UV applications or advanced lithography, such as, VUV applications. Even further still, there is a need for a method of manufacturing a pellicle which does not result in a membrane including conventional materials.
An embodiment relates to a thin film pellicle for integrated circuit fabrication equipment. The pellicle includes a film relatively transparent to radiation having a wavelength of less than 180 nanometers and a frame. The film has a periphery and a center portion. The frame is coupled to the periphery of the film and is exclusive of the center portion. Radiation can be transmitted through the center portion.
Another embodiment relates to a pellicle for fabrication equipment. The pellicle includes a means for allowing radiation to pass and a frame coupled to the means for allowing the radiation to pass. The means for allowing radiation to pass includes silicon.
Yet another embodiment relates to a method of manufacturing a pellicle. The method includes forming a film on a polymer substrate and attaching a frame to the film. The polymer substrate is removed from the film.
Still another embodiment relates to a method of forming a pellicle relatively transparent to VUV radiation. The method includes growing a relatively transparent film on a polymer substrate and removing the polymer substrate.